Charging of accumulators from a variable-speed dynano electric machine.



Y J. G. P. THOMAS.

CHARGING OF ACCUMULATORS FROM A VARIABLE SPEED DYNAMO ELECTRIC MACHINE. APPLICATION FILED MAR.23, I914.

1,272, 148. Patented July 9,1918.

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O E. M. F. of the battery UNITED STATES PATENT OFFICE. v

JOHN GODFREY PARRY THOMAS, 0F CHIS'WICK, LONDON, ENGLAND, ASSIGNOB, T0 THOMAS FOREIGN PATENTS LIMITED, OF KENSIIN'G'ION, LONDON, ENGLAND, A

CORPORATION OF GREAT BRITAIN.

CHARGING 0F ACCUMULATORS FROM A VARIABLE-SPEED DYNAMO-ELECTRIC MACHINE.

Specification of Letters Patent.

Application filed March 23, 1914. Serial No. 826,740.

To all whom it may concern:

Be it known that I, JOHN GODFREY PARRY THOMAS, a subject of the King of Great Britain, residing at 21 Ennismore avenue,

in the county of London, England, have invented new and useful 1mprovemcnts in the Charging of Accumulators from a Variable-Speed Dynamo-Electric Machine, of which the following is a specification.

- This invention relates to electric generating systems, and its purpose is to provide a system by which substantially constant output is derived from a dynamo electric machine driven at variable speed.

A further object of said invention is to apply to the field winding of an electric generator, the armature of which is bridged across a battery, an E. M. F. opposing the and varying with thespecd of the machine.

By way ofillustration of the invention a system is hereinafter described in which a two-pole generator is utilized. A diagram 5 of connections of this system is shown in the accompanying drawings.

The main brushes 10, 10 of the armature 11 are connected directly to the battery 12. The field winding 13 is of the series type and therefore of very low resistance and is connected between one of the main brushes l0 and a brush 14: adjacent to it.

To prevent sparking at the brushes 1%, 15 the pole cores 16 may be cut away opposite the conductors to which the brushes are for the time being connected. The field should be so designed that the iron is far from saturation.

The machine is so designed that when a certain minimum speed is exceeded the field is sufiiciently excited to produce an E. li L F. a little in excess of that of the battery. The portion of the armature winding between the brushes 14 15 and the more remote brush 10 may be regarded as a motor armature under certain conditions, and in conjunction with the field winding constitutes a series motor, generating a back E. M. F. which in the field circuit opposes the terminal voltage of the generator. Thus assuming the left hand brush 10 to be removed from the commutator for a moment, it will be obviousthat this series motor is simply driven from the battery, used for starting the prime motor by which the generator isto .be driven. Since the field resistance is practically negligible the E. M. F. between the right hand brush 10 and the auxiliary brushes 1a, 15 will always be substantially the E. M. F. of the battery Whatever the speed. And therefore when the machine is operated by the prime motor and the left hand brush 10 is replaced on the commutatonthe E. M. F. between the brushes 10 when both of them are on the commutator will always'slightly exceed the E. M. F will be capable of charging the battery. The portion of the armature winding between the auxiliary brushes and theright hand brush 10 carries less current than that between the brushes let 15 and the adjacent brush 10, the difference being and in this condition can be the amount of the field current. It is obvlously essential to the invention that the field resistance should be exceedingly small, as it is necessary that the E. M. F. between the auxiliary brushes and the right hand brush 10 shall always be practically the battery E. M. F.

A steadying resistor 17 is inserted between the left hand brush l0 and its connection to the field and battery, that is ina position to carry both the charging current and the field current.

It is possible that the regulation is secured by means of resistor 17, and its connections, for the following reasons: The current through resistor 17 is the sum of the current in the battery branch and the branch which includes field winding 13. The cnrrent through the battery branch will increase at a greater rate than the increase of voltage applied thereto with any increase of speed. The reason for this is well known and is due to the low internal resistance and constant back elect-romotive force of the battery. The current through the field branch tends to increase proportionately with the voitage applied thereto. Any increase in drop across resistor 17 will tend to decrease the field current and, as above pain out,

i'ect of the armature, owing to the regulating the drop across resistor 17 will increase taster than the machlne voltage tends to 1ncrease by reason of the tendency of the current in the battery branch to increase disproportionately.- It then, the battery component of current in resistor 17. increases as i stated, the field current component may be nade to decrease as the speed increases.

It. is to be noted that the auxiliary brushes are quite close to one main brush and by no means disposed in the middle of the field or anywhere in the neighborhood of the axis of the field. Consequently though the of the field may shift a little on account of the cross magnetizing efeii'ect above described of the resistor 17 ,this shifting will be very slight and it will never shift past the auxiliary brush. sign of the E. M. F. applied to the field will never be changed by variation of load, nor will its magnitude vary largely with the load. The subject of the invention istheremachine, while with a battery it will oper- It will also work equally well upon batteries ate with practically constant voltage.

of difierent voltage so long as the voltage is Thus theravages not such that the iron of the field becomes saturated.

What I claim is:

1. A generating system, comprising a dynamo electric generator, having an armature winding and low resistance field windsaid armature, a commutator with main brushes thereon, a battery connectedacross said main brushes. an auxiliary'brushad I jacent one of said main brushesconnections joining the whole of said field winding between said auxiliaryibrush and the neighboring main brush, and a regulating or steadying resistance connected to the main brush in circuit with the battery and with the field winding. I In testimony whereof I haye signed my name to this specification in the presence of two subscribing witnesses;

JOHN GODFREY PARRY THOMAS; Witnesses:

A. E. Onmn, LEONARD HAYNES. 

